In recent years, mobile wireless communication terminals have been used in every situation with development of a wireless communication technology. The wireless communication terminals may be required to perform highly reliable data transfer even in a mobile environment where mutual intermittent network connection is impossible. As such a network control method, a Delay/Disruption-Tolerant Network (DTN) is known. The DTN is a method of relaying and transmitting data to other communication terminals while accumulating data to be transferred in each communication terminal.
The DTN includes epidemic routing, as one data transfer method, which is disclosed in, for example, PTL 1. The epidemic routing is a data transfer method in which a communication terminal, connected with another terminal by means of wireless communication, propagates data, while complementing difference data based on information about data held by each terminal.
Herein, a specific example of a data transfer method of the epidemic routing will be described with reference to FIG. 1A and FIG. 1B. FIG. 1A illustrates a Pull-type data transfer method of the epidemic routing.
First, wireless communication terminals_A and B are connected with each other by being located within a range of short-range wireless communication. Then, the wireless communication terminals_A and B exchange a message (hereinafter, a Summary Vector Message (SVM)) including a Summary Vector that is a list of contents (held information) being data stored in the own terminal (Step S1). Accordingly, each of the terminals_A and B can grasp data that the own terminal does not hold yet the counter terminal holds. Then, in the example of FIG. 1A, the terminal_B requests, based on the SVM, the terminal_A for data that the terminal_A holds yet the own terminal_B does not hold (Step S2). In response to this request, the terminal_A transmits contents being the data that the own terminal_A holds to the terminal_B (Step S3). Accordingly, the terminal_B can hold the data that the terminal_A holds, and can synchronize data mutually with the terminal_A.
In addition, FIG. 1B illustrates a Push-type data transfer method of the epidemic routing. First, terminals_A and B are connected with each other by being located within a range of short-range wireless communication. Then, the terminals_A and B exchange an SVM similarly as described above (Step S11). At this time, it is assumed that there are data that the terminal_A holds yet the terminal_B does not hold. Then, the terminal_A transmits, based on the SVM, data that the terminal_B does not hold to the terminal_B (Step S12). In other words, in the Push type, the terminal_A transmits data to the terminal_B even without a request from the terminal_B, unlike the above-described Pull type. Accordingly, the terminal_B can hold the data that the terminal_A holds, and can synchronize data mutually with the terminal_A.
Then, the epidemic routing described above is preferably used in an ad-hoc mode as a wireless network setting under an environment where wireless communication terminals are freely movable. This is because wireless communication terminals in the ad-hoc mode are capable of forming a peer-to-peer link by using short-range wireless communication even without existence of an access point. In addition, wireless communication terminals in the ad-hoc mode need no association establishment and perform fast session establishment.
In this manner, use of the epidemic routing in the ad-hoc mode allows to relay and transmit data within moving wireless communication terminals by means of short-range wireless communication while accumulating the data in the wireless communication terminals. It also becomes possible to transmit data to a distant terminal. For example, as illustrated in FIG. 2, even in a situation where there are wireless communication terminals such as movable portable telephone terminals_A1 to A6, it is possible to transmit data to another neighboring wireless communication terminal by means of short-range wireless communication, as illustrated with arrows in FIG. 2. For example, even if it is impossible, between the terminal_A1 and the terminal_A6, to directly communicate with each other by means of short-range wireless communication, it becomes possible to synchronize data eventually after relay transmission via the other terminals_A2 to A4.